Feeding and Nutrition of Reptiles

As the Millenium approaches, the 1990's have seen the introduction of reptiles into the mainstream pet trade and they have managed to work their way into millions of homes as common household pets. Once owned by a few hobbyist or "the kid down the street". These amazing animals have worked their mysterious magic on adults and children alike and are fast becoming as common as fish or birds in millions of households. As a result of captive breeding projects and easier availability through the pet trade many new and unusual species are finding there way into the hands of pet owners.

As a result of this newfound popularity and ease of availability many problems are beginning to arise with captive reptiles. One of the most common problems seen with captive reptiles is nutritionally related disorders. This is a direct result of the fact that little information is available on the proper feeding methods of many species. This is a problem that is closely related to the fact that the demand for captive reptiles as pets has grown faster than science's knowledge of their needs.

While many species are still considered to be exotic, many species such as the ball python or the (Giant) green iguana have earned a place as common pets in most pet stores. Even with their newfound popularity there is still a lot that needs to be learned and addressed concerning their proper care and feeding. There are many misconceptions surrounding proper feeding and nutrition of reptiles. Often time's foods for reptiles are developed with little testing or scientific data to back them up, in fact many times these foods even prove harmful to the animals that are eating them. This is most likely the result of the varying needs of the many different species and their dependency on temperature ranges, humidity and digestive metabolic adaptations.

With these facts in mind it is the author's intent to provide the reptile owner with the necessary information to properly understand the nutritional needs of their reptile and the proper methods and foods for feeding it. This book includes sections on nutritional requirements of herbivorous, carnivorous, omnivorous and insectivorous reptiles. It also contains information on nutritionally related disorders and metabolism. Methods for storing and offering foods are also included.

As stated the information contained in this book are current at the time of its printing. Much of this information is the result of recent veterinary and scientific studies on the nutritional needs of reptiles. Given the ever growing need for knowledge and understanding for the proper nutritional needs of reptiles, owners are encouraged to stay informed and abreast of changes and new research. Joining a herpetological society in your area and staying in touch with other reptile owners to discuss and share information may best do this. It would also serve an owner well to take the time to investigate the nutritional needs and demands of each individual species that they intend to keep.

An important factor in understanding proper nutrition is an understanding of the fact that a reptile's nutritional needs are greatly effected by its metabolism and its metabolism is greatly effected by its diet. It is critical to proper nutrition to understand the vital link between these two factors. Each species has its own distinct metabolism, which is dictated by its evolutionary design. It is possible for two separate species to have evolved on opposite ends of the earth and act and appear very similar, but their dietary needs may vary greatly. This is a result of years of evolution based on the food sources available and the temperature variations in each species own geographical location. As a result two similarly looking species of lizards may exhibit opposite dietary needs, one may be carnivorous while the other may be herbivorous.

Variations in temperature play a key role in the metabolism of reptiles. This a result of there ectothermic nature and their dependency on environmental temperatures. A reptile's metabolic rate determines the amount of food that it requires to live and move about. It is this dependency on environmental temperatures rather than an internal metabolism that creates a problem for most owners of captive reptiles.

If a captive reptile is kept at sub-optimal temperatures and fed too much it may cause anorexia due to the reptile's lack of activity caused by the cooler temperatures and lowered metabolic rate, which cause improper digestion while being maintained on a constant diet. The same is also true for reptiles that are kept under conditions that are too warm and are under fed. These reptiles will continue to increase in movement as their metabolic rate increases and continue to burn energy faster than it is being supplied. Illness, reproduction and growth may also equally effect metabolism.

The frequency of feeding depends greatly on the metabolic rate, as mentioned earlier. Active species, like garter snakes, will require more frequent feedings than will less active species, like boa constrictors. The nutritional qualities of the foods being offered will also play a role in the required frequency of feeding. Less nutritious foods will need to be fed more frequently and in greater volumes than those that are more nutritionally balanced for a particular species.

Species like garter snakes and racers may be fed once weekly, if maintained at proper temperatures, while species such as geckos, anoles and iguanas should be fed four to five times a week. There is a reduced risk of these animals becoming obese in captivity as a result of their higher metabolic rates and may be fed more frequently as a result. Some species of aquatic turtles, while they may present the appearance of a slow metabolic rate, actually have a higher rate and require feeding on a daily basis.

Large bodied constrictors and vipers, such as Burmese pythons or diamondback rattlesnakes have a higher risk of becoming obese in captivity as a result of their slower metabolic rates. They should be fed once every 4-6 weeks, compared to desert tortoises and box turtles should be fed smaller amounts of concentrated meals daily.

Larger lizards like the Gila monster and the Savannah monitor should be fed once or twice a week. They should be offered large amounts of food items at each feeding. The same is true of most crocodilians, which should also be fed large amounts once or twice weekly. The only exception to this rule is the gharials, which eat a diet consisting of fish that has a high water content and should be fed every two days or so as a result.

In order to properly determine the frequency of feeding for a given species an owner must first determine the energy requirements of that particular species. As a general rule smaller species will have a higher metabolism than will larger animals.

Many owners are under the mis-conception that their reptiles must be fed a diet of live prey items. Many carnivorous reptiles will readily accept pre-killed prey. This method of feeding offers many advantages over feeding live prey items.

In the wild, reptiles eat live prey, so why is it a problem to feed them live prey in captivity? The answer is very simple. Live prey in the wild has a means for escape if the reptile does not consume them. In captivity, prey items are confined to a limited space and if not consumed right away, will fight for their lives or eventually become hungry and turn the reptile predator into their food source and prey. This creates a problem for the captive reptile that will usually avoid fighting back at all or fight back with limited means to defend itself. The end result of this conflict for most reptiles ranges from minor bite wounds to severe or fatal injuries.

Feeding pre-killed prey presents not only a safe method for feeding, but a humane means of disposition for the prey item. The prey is spared from having to be forcefully disposed of slowly or eaten alive.

Captive bred and born reptiles may be easily started on pre-killed prey from birth with little effort. Wild and imported reptiles may require a little more effort on the part of the owner to switch for live to pre-killed prey. One method for switching a reptile from live to pre-killed prey is to offer it a live food item followed by a stunned food item in the same feeding. The next feeding should consist of a stunned food item followed by a pre-killed food item. The process may take several feedings over a period of months, but eventually the reptile will adjust to the new diet of pre-killed food items.

Storing food for reptiles can be a very simple process, but there are some factors that effect the storage method involved. Live food items, such as rodents should always be purchased live or freshly killed and then frozen. It is important that they be frozen shortly after killing them. Many sources currently offer frozen rodents through mail order. The problem with purchasing rodents from these sources is that in most cases it is difficult to determine how long the rodents have been frozen for. The method of freezing food items is fine, but the vitamins and minerals will begin to breakdown after about 3 weeks. By purchasing and freezing fresh food items yourself you are able to know just how long the food has been frozen for. Freezing is a good way to store food items and as an added benefit the process of freezing will kill most parasites that the prey item may be harboring, both internal and external.

Plant matter is best served fresh and may be stored under refrigeration without a problem or breakdown of vitamin and minerals. Store bought frozen fruits and vegetables present the same problems with vitamin and mineral breakdown that are present with rodents and the duration of freezing. Given the low cost and availability of fresh fruits and vegetables there is little reason to justify not feeding them in place of higher costing commercial or frozen foods.

Insect prey is one of the most problematic forms of foods to store. Most insectivorous reptiles require frequent feedings and a ready supply of fresh food items. The most effective and least expensive way to store this type of food item is to purchase live insects and to breed and raise your own. Raising your own takes little space and equipment and allows an owner to provide the insects with a vitamin-supplemented diet that will benefit their reptiles. This method also provides an owner with a food source that may be feed at any time without having to run down to the local pet store to discover that they are sold out. It should be noted that when purchasing insects for food items that these items should be obtained from specialty dealers or pet stores and NOT from a local bait and tackle shop. The difference between the two sources is the types of foods that are fed to the insects. Insects that are specifically raised for feeding to reptiles are usually fed a diet that is higher in calcium.

There are four basic food preferences among the countless species of reptiles. A carnivorous diet consists of meats, an insectivorous diet consists of insects, a herbivorous diet consists of plant matter and an omnivorous diet may consist of a combination of the other three groups. While each species has its own unique dietary requirements, their preference for specific food items is largely based on its natural geographic location and the types of food items that are readily available in that location. Over time each species has developed a genetic preference and digestive system for a given food item based on this availability of food within a geographic location. These four basic diets may be broken down into two separate groups. Those, which consist of animal proteins and those that consist of plant proteins.

The first group would include food items made up of vertebrate and invertebrate prey items. Vertebrate food items for reptiles are made up of mammals, birds, other reptiles, and amphibians. Well-fed vertebrate prey items provide a reptile with a complete and balanced diet. Reptiles receive many amino acids, vitamins and minerals from the muscles, organs and bones of vertebrate prey. Invertebrate food items commonly fed to captive reptiles include crickets, mealworms and waxworms. These items lack some essential vitamins and minerals an often require supplementation. An example is a lizard that is fed a diet that consists of crickets. Crickets contain high amounts of protein but lack essential calcium.

The second group would consist solely of plant matter, such as leaves, fruits, vegetables, flowers and berries. Reptiles that fall into this group are very specialized in the types of plant matter that they consume. Desert species may consume hays and drier foods while tropical species may prefer colorful fruits and vegetables. While all reptiles require protein it is important to note that there are two very distinct types of proteins, as mentioned earlier. It is a common misconception by reptile owners that all proteins are the same. Herbivorous reptiles require plant proteins and are often mis-fed animal proteins in captivity in the form of dog chows or trout chows. These animals have very specialized digestive systems that are not designed to break down and process animal proteins. Proteins, while important in herbivorous reptiles, is less important than for reptiles that consume vertebrate and invertebrate prey.

Snakes can be either carnivorous, insectivorous or both, but they are NOT omnivores because they do not consume any plant matter at all. Many snakes have a preferred staple of their diet, but they will consume other food items when presented with the opportunity or need to do so. Some snakes have very specialized eating habits and are designed to eat specific prey. An example of this is the Egg eating snake (Dasypeltis scabra), which has a specially designed spine that allows the snake to spit an egg open inside its body, remove the yolk and then regurgitate the shell. Even though the Egg eating snake is designed to eat eggs it will accept other food items if the need to do so arises. This is not always the case, for example the King Cobra will only feed on other snakes and will refuse to accept anything else. For this reason it is important for a reptile owner to know the specific needs of the species that they keep and the food items that they will except when their preferred prey items are unavailable.

Snakes have an extremely simple digestive system that involves a duct that starts at the mouth and runs to the cloaca. To put it another way, it is a "straight shot" from point A to point B. As a result of this simple digestive tract the digestive process starts with the enzymes in the mouth. Over the centuries these enzymes have evolved into venom in some species. Venom plays a key role in digestion, which is its primary function, and is only used as a defense when necessary. A venomous snake would much prefer to digest its meal than to waste its venom on defense. This is not to say that a venomous snake is harmless, it is just an example of the over play on the misunderstandings surrounding reptiles. Venomous snakes have been known to bite without injecting any venom at all into the victim, this is a result of conserving venom for digestion and using it defensively as a last resort. (The author does NOT recommend or condone the keeping of venomous species by private owners and breeders and recommends that they be kept and studied by institutions ONLY.)

The stomach of snakes is a muscular organ in which, the digestive process continues. After leaving the stomach the remains pass through the small intestines, which are much less coiled than in mammals and birds. The small intestine then empties into the colon where feces and urates are stored until they are expelled as wastes.

Lizards are a very diverse group and may consume both plant and animal proteins depending on the species. They may be carnivores, insectivores, omnivores or herbivores. Many species may start life by consuming animal proteins in the form of insects and switch over to eating only plant proteins later in life. Some lizards, such as the (Giant) Green iguana have very specialized needs and often suffer nutritionally related illness in captivity as a result of being fed an improper diet. Knowing the specific needs of your lizard will help to avoid nutritionally related illnesses from occurring. Of the four groups of reptiles, snakes, lizards, chelonians and crocodilians, lizards are the one group that appears to be at the highest risk of nutritionally related illnesses. This is most likely the result of their diverse diets and nutritional mis-conceptions or mis-information on the part of owners.

Lizards have a very simple and elongated stomach. Some species are known to voluntarily consume rocks to help grind food within the stomach. While this is normal it may lead to complications with the digestive tract. Lizards that exhibit this behavior are usually being kept at sub-optimum temperatures. This behavior is more commonly seen in captive reptiles as opposed to wild lizards and is most likely the result of the temperatures that the animals are being provided with.

Herbivorous species like the green iguana, chuckwallas and the prehensile tailed skink all have a sacculated colon that is used in the process of hindgut fermentation. Lizards with this type of digestive system require higher temperatures to enhance the fermentation process that often involves the aid of symbiotic parasites that play a vital role in the fermentation process.

The final stop in the digestive process is a group of chambers. The coprodeum is used to store feces. The urodeum is used to store urinary wastes and the proctodeum, which is, were all wastes are held until they are eliminated. These chambers are present in all species of lizards regardless of their dietary preference.

Chelonians are a very diverse group, as are lizards. This group is made up of carnivores, insectivores, herbivores and omnivores. They consume both animal proteins and plant proteins. Species like Sea turtles consume food items made up of animal proteins, in the form of fish, as young and switch to a diet of plant proteins at the on set of sexual maturity. Sea turtles are also known to consume coral. Tortoises usually eat a diet made up of plant proteins from birth to death. These examples help to show the diversity of diets among the different species that make up this group of reptiles. Despite the diversity of food preferences all chelonians kept in captivity should be fed on a daily basis.

A unique trait of this family is the lack of digestive enzymes produced by the salivary glands. Instead the stomach, small intestine, liver and gallbladder produce these enzymes. The small intestine is also responsible for the absorption of nutrients and water from the food.

Herbivorous chelonians have a digestive tract that allows for the microbial fermentation of plant matter in the large intestine. This type of digestive system, as well as all others in reptiles, is greatly effected by temperature. Unlike their lizard counterparts chelonians have a less developed cecum which results in the fermentation process taking place in the large intestine, rather than the hindgut.

This group of reptiles is carnivorous and rarely, if every will consume plant matter. Interesting variations in diet among crocodilians includes the gavials and false gavials, which feed exclusively on fish. As a result of their unique diets gharials should be fed whole fish to include bones. This provides the animal with sufficient amounts of calcium from the bones of the prey item. If fed parts or frozen fish, the food should be supplemented to compensate for the lack of bone derived calcium.

Feeding these amazing animals should only be done on an individual basis, as they will feed without regard for any other crocodilians around them and in some cases cannibalism may occur.

Crocodilians may stop feeding if the temperature drops below 75 degrees F. They have a very specialized stomach that is divided into the corpus and the pars pylorica to form a type of gizzard, much like that of a bird. Food is ground up in this "gizzard". The stomach is highly acidic and capable of digesting a wide variety of food items. The gizzard plays a significant role in the digestive workings of the stomach due to the animal's lack of chewing its food. Digestion in crocodilians is a very complex and highly efficient process.

The Tuatara is an extremely rare species that is never found in private collections and is only rarely kept by institutions. This species of reptile is very unusual, so unusual in fact that it is NOT classified as a member of any of the four families of reptiles, but has a family all its own. The existence of the animal dates back too prehistoric times and has remained unchanged by evolution since that time. Little is known about this species and it is not available to private owners, but because of its existence as a reptile it will be noted here.

Tuatara (Sphenodon punctatus): feeds on crickets, silk moth larvae, pinkie mice and quail chicks in captivity. Little is known about it diet in the wild. Due to the rare nature of a captive Tauatara, they are only fed carefully cultivated and raised prey items to avoid nutritionally related disorders and the transmission of parasites. Don't look for this species in your local pet store or reptile exposition.

We as humans tend to think that when it comes to taking and giving vitamins that more is better. This is a misconception that causes complications and related illnesses in captive reptiles. While many species require supplementation of vitamins and minerals it is important to monitor the amounts that are given. If maintained on a proper diet many species do not require any supplementation at all. When adding a supplementation to a well balanced diet an owner runs the risk of overdosing the reptile on vitamins. When given in proper amounts vitamin and mineral supplementation has its place in reptile husbandry, but overdosing can lead to toxicity and related disorders and illnesses. Given the supplements and the forms that they are sold in, it is hard to properly monitor the amounts that are being given. While many books and breeders advocate the use of supplementation with all captive reptiles this is NOT the case. Only reptiles that consume a vitamin or mineral deficient diet require carefully monitored supplementation.

When calcium and vitamin D3 are provided in excess the plasma calcium level is increased. This leads to the formation of calcium rich mineral salts in soft tissue. The tissues that are effected are the heart muscles, airways, intestinal tissues, which are very sensitive to this excess of mineral salts.

Providing protein in large amount, or of the wrong type, may lead to mineralization as well and while it may serve to increase growth, it is not without its price. In older animals this excess may cause kidney and liver problems.

Proper supplementation or the lack thereof, is best done by knowing the nutritional needs and diet of a specific species. Random guessing and routine supplementation is an improper way to dose vitamins and mineral. Remembering that vitamins and minerals should be handled as if you were giving a prescription drug will help to avoid vitamin and mineral deficiencies and over supplementation.

Consumption of feces is a common and normal behavior in some species of reptiles. Most owners look at this as merely a disgusting behavior and are unaware of the fact that it is a necessary step in the developing digestive systems of some species. The reason for caprophagy is not behavioral but is related to the transmission of needed microorganisms that aid in the digestive process of some species. This is most commonly observed in green iguanas (Iguana iguana) and other herbivorous species. Young animals that perform this behavior should be allowed to do so, but it should be discouraged in adults to prevent the spread of harmful parasites and bacteria.

Understanding proper nutrition is the key to a healthy captive reptile. Knowing the proper diet and temperature combined with an understanding of the specific needs of a given animal greatly increases its chances for a long and healthy life. Nutrition and feeding can have a dramatic impact on the health of your reptile and taking the time to learn how your reptile's body works will greatly help in understanding its dietary needs.

Given the fact that we as humans have a very hard time understanding our own dietary needs it does not come as a surprise that we have a difficult time understanding the sometimes complex nutritional needs of reptiles. Their diversity among the different species presents many complications and challenges for anyone who would keep them as pets. The fact that reptiles have been on this earth far longer than humans, it is surprising to see that until reptiles where kept in captivity the largest danger that they faced were from predators. In captivity the largest danger that a reptile faces is nutritionally related illnesses.

Joining a Herpetological group in your area, or nationally, will greatly help in learning about the specific needs of a given species and the proper ways to provide your reptile with those needs. Remember that the way to a reptile's heart and health are through its stomach.

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